textproduct: Rapid City

KEY MESSAGES

- Light snow today and Tuesday with the highest accumulations over the northern Black Hills - Warmer mid-week - Arctic air Friday into next weekend

DISCUSSION

(Today Through Sunday) Issued at 125 AM MST Mon Jan 13 2025

08z surface analysis had stationary front from eastern MT to eastern CO. Stubborn low clouds/fog from KRCA-KIEN per surface observations/nighttime microphysics RGB, which should dissipate this morning. Water vapour loop had upper low just north of MN with cyclonic north/northwest flow from central Canada into the northern Plains. Several disturbances noted in the flow, which will be our main short term forecast concern.

Today/Tuesday, upper low slips into the Great Lakes today and then zips east Tuesday. It will push a couple of shortwaves through the CWA with each one bringing weak QG/frontogenetic forcing, particularly along the stationary boundary in place. Moisture is limited, but could seen 1 to locally 2 inches of snow on the plains over the next 48 hours. Boundary layer flow supports Froude numbers >1 and 0-2km RH >90% over the northern Black Hills from ~15z today to ~18z Tuesday. HREF has 50% chance >0.40" QPF over the highest elevations of the Black Hills and 70-90% chance 0.25" QPF. Looks like a good recipe for 4-8" of snow. Bufkit soundings depict a bit more westerly component, so highest totals will be between Cheyenne Crossing, Buckhorn, and Moskee. Winter Weather Advisory hoisted to account. Temperatures will be near guidance.

Wednesday/Thursday, east/west-oriented upper ridge pushes warm front through the CWA promoting downslope flow. Mild temperatures expected, particularly on the eastern slopes of the Black Hills/adjacent plains where 50F is in reach per ensemble guidance.

Friday/next weekend, confidence is high that deep upper trough develops over the eastern 3/4ths of North America opening the door for arctic air to spill into the northern Plains. Some light snow will occur. Temperatures will be 20-30F below normal but the coldest air will be east of the CWA. Apparent temperatures may be cold enough for the issuance of Extreme Cold products, but right now, record-breaking cold is not on tap per EFI/NBM guidance. Just some good old fashioned January weather.

AVIATION

(For the 12Z TAFS Through 12Z Tuesday Morning) Issued At 411 AM MST Mon Jan 13 2025

Light snow will expand eastward from northeastern WY and the Black Hills into the western SD plains through today. Widespread MVFR/LCL IFR conditions will prevail over northeastern WY, the northern BH, and northwestern into south central SD through most of today. Conditions at KRAP expected to remain mostly VFR this afternoon, though MVFR CIGS and -SN may affect the terminal from time to time; confidence in timing, however, is too low to mention in TAF.

UNR WATCHES/WARNINGS/ADVISORIES

SD...Winter Weather Advisory from 8 AM this morning to 11 AM MST Tuesday for SDZ024. WY...Winter Weather Advisory from 8 AM this morning to 11 AM MST Tuesday for WYZ057.